1. Field of the Invention
This invention relates generally to safety belt retractors having a locking device for preventing protraction of a safety belt when the vehicle is undergoing a velocity change in excess of a predetermined magnitude.
2. Description of the Prior Art
Most vehicles, especially automobiles, are equipped with safety belts in order to restrain a passenger in his seat when the vehicle is undergoing a substantial change in velocity, such as when the vehicle is involved in an accident. In order for the safety belt to be effective, the belt must be locked into position to prevent protraction of the belt during the vehicle velocity change. For example, if an automobile decelerates rapidly because of an impact, the passenger will be thrown forwardly due to inertia and will apply considerable force against the safety belt. Therefore, in order for the belt to be effective, it must be locked in position to prevent movement of the belt during this deceleration.
It is to be understood that where the term "change in velocity" is used throughout the application, the term shall be interpreted to mean change in velocity in a relatively short interval of time as would be encountered, for example, in a crash situation or a sudden emergency stop.
Present day retractors such as disclosed in U.S. Pat. No. 3,838,832 owned by the assignee herein, permit continual protraction and/or retraction of the belt after it is positioned around the passenger and during the entire period that the vehicle undergoes changes in the velocity less than a predetermined dangerous amount. The passenger is thus afforded freedom of movement without having to unbuckle the belt and completely retract the same. However, when the vehicle undergoes a velocity change in excess of the said predetermined amount, the locking device is rendered operative to prevent further protraction of the belt and restrain the passenger in his seat.
More specifically, the retractor disclosed in the aforesaid patent permits protraction of the belt while the passenger places the belt around himself, and upon release of the belt, the retractor draws the belt snugly against the passenger. Retractors of this type have a shaft rotatably mounted on a frame and around which the safety belt is wrapped for protraction and retraction with respect thereto. A bias spring urges the shaft to rotate in a direction to wrap the safety belt around the shaft. The retractor also includes a ratchet drivingly connected to the shaft and operatively associated with a locking device to prevent protraction of the safety belt at certain predetermined times.
The known locking devices may be of the type comprising a pendulous mass which is responsive to a change in vehicle velocity, including any change in vehicle direction. The pendulous mass is mounted so that it is moveable between a first position wherein the change in vehicle velocity is below a predetermined magnitude, and a second position wherein the change in vehicle velocity is greater than said predetermined magnitude to effect operation of the locking device.
The known structure further provides for a pivotally mounted pawl which is capable of movement from an inoperable position wherein said pawl is spaced from the ratchet by a preselected distance to an operation position wherein said pawl engages the ratchet to prevent protraction of the belt. The pawl is also operatively associated with the mass such that movement of the pawl is responsive to the position of the mass. The arrangement is such that when the mass is in its second position, the pawl is displaced to its operate ratchet engaging position to prevent protraction of the belt.
Since the safety belt retractor locking device is intended for use on vehicles of different manufacturers, each having different specifications on the magnitude of the change in velocity considered dangerous to effect operation of the locking device, it was heretofore extremely difficult, if not impossible, to design a generally universal type locking device suitable to satisfy the needs and requirements of all the manufacturers. For example, the spacing between the pawl and the ratchet, when the pawl is in its inoperative position, is preselected in accordance with the customer's specification to obtain the desired level of sensitivity of the locking mechanism. In this regard, the said spacing may vary between 0.018 inches (0.046 cm.) and 0.042 inches (0.107 cm.) depending upon the desired level of sensitivity.
It will be appreciated that since movement of the pawl is a function of the pivotal movement of the mass, then the extent to which the mass pivots in displacing the pawl to its operative ratchet engaging position is a function of the preselected spacing between the pawl and the ratchet. Accordingly, once the spacing between the pawl and the ratchet is determined from the customer's specifications, the position of the mass is similarly readily determined for that specific application of use. The spacing between the pawl and the ratchet is very crucial, and precise measuring equipment is necessary to insure that the component parts of the locking device are manufactured within acceptable tolerances.
In those instances where the mass is pivotally supported within an opening or well of the frame structure, the dimensional limitations of the well are fixed in order to locate the mass in the determined position. It will thus be appreciated that the fixed dimensions of the well, or other supporting structure for the mass, will be different for each specific application of use as determined from the position of the mass required to satisfy the customer's specifications. Accordingly, it was usually necessary to design a separate locking mechanism having specific tolerances for each application of use. The present invention substantially reduces the number of separate locking mechanisms required to satisfy the varied requirements of all automobile manufacturers. In this regard, it is within the purview of the invention to provide a single locking mechanism operable within a range of levels of sensitivity to satisfy the specific requirements of most of the automobile manufacturers.